Preheat oven to 375° F.
Sauté sausage, onion and salt in oil in a large skillet until meat is browned and liquid has evaporated. Add 1 cup pasta sauce and set aside. In a bowl, combine ricotta cheese, ½ cup mozzarella cheese, 2 tablespoons Parmesan cheese and egg; set aside. Spray a 9-inch square baking pan with vegetable spray and spread ½ cup sauce on the bottom of the pan. Layer ⅓ the sweet potato “fettuccine”, ½ cooked turkey mixture, ½ package spinach and ½ the ricotta cheese mixture. Repeat layering. Top with remaining sweet potato “fettuccine” and remaining pasta sauce. Top with remaining mozzarella and Parmesan cheeses.
Bake 60 minutes. Let stand 10 minutes before serving.